It is widely accepted that the colour coding labelling of file folders of a filing system significantly improves the efficiency of the system. Such systems may be that as described in U.S. Pat. No. 3,504,907. File labelling techniques have been recently improved where, for example, in a colour coded system, the labels may be machine read to facilitate electronic control of the filing system. Such a system may be that as described in copending U.S. patent application Ser. No. 775,687. In order to apply labels to folders, it is important to ensure accurate placement of each label on the folder to present a proper colour scheme along folder edge in the colour coded filing system.
An apparatus for applying labels to folders is disclosed in U.S. patent application Ser. No. 830,118. In that system a file folder is placed on a conveyor, the folder is conveyed past a plurality of labellers and, in accordance with a predetermined program, the labellers are controlled to apply a series of labels to the folders. When the folder is discharged from the labelling apparatus, the series of labels is in accordance with a predetermined scheme to present the desired colour array along folder edge. The conveyor of the labeller disclosed in that patent application uses a pair of clamps to grip each folder, which is placed on the conveyor, and hold the folder during application of labels to it. Although the clamps of the conveyor system are satisfactory for ensuring accurate holding of a folder, problems have arisen with respect to maintenance of the conveyor clamp, wear and tear on the conveyor belt which carries the clamp due to opening and closing of the clamps causing flexing of the conveyor belt at its joints and the inability to operate at higher speeds for labelling folders.
Other approaches to clamping thin articles on a conveying mechanism are disclosed in Canadian Pat. Nos. 576,390 and 1,006,194. The latter Canadian patent discloses the use of a spring clamp system, where the spring is used to maintain the clamp in its normally open position. A cam arrangement is used in combination with a roller secured to the clamp jaw arm to draw the clamp shut and, by use of a pawl, hold the clamp in the closed position against the opening force exerted by the spring.
In Canadian Pat. No. 576,390, a clamping mechanism is disclosed having a pivoted clamping jaw which is urged to its closed position by a tension spring, which acts on a laterally moveable U-shaped arm. The U-shaped arm has a depending roller which is engaged by a cam to move it laterally of the conveyor to either open or close the pivotally mounted jaw. A continuous length of cam must be provided to maintain the clamps open at needed locations along the conveyor. Due to the linkage mechanism arrangement, a relatively large tension spring must be used to exert sufficient clamping force to secure sheet-like material to the conveying mechanism. The arrangement, due to the linkage, is complex and susceptible to frequent maintenance and breakage. In addition, it adds to the bulkiness of the conveyor and increases the lateral extent of the conveyor, because the U-shaped arms envelope the side of the conveyor.